Yet another article on a tubeless tire blowing off the rim.

[Clancy]

Interesting article on yet another tubeless tire blow-off. But Zenn theorizes the rim, not the tire, maybe at fault and being set-up tubeless was not part of the issue. Also interesting, given the recent tread on Challenge tires, that he turned to their engineer for explanation.

I’m not sure what to think anymore.

Are aluminum rims with tubed tires the only way to go? Or sew-ups which I’m not doing.

https://www.velonews.com/2019/09/bikes-and-tech/technical-faq-a-tubeless-tire-blowout-in-the-pyrenees_500757

[weiwentg]

Well, the article did say that some carbon rims can have sharp edges on their bead hooks. They're supposed to be sanded off after the rim is molded (the molding process inherently will leave sharp edges). The guy who Zinn consulted blames the incident on a sharp edge or burr that someone missed. We could just inspect all carbon rims for burrs, no?

That said, the engineer in question works for Challenge (note: the tires in Zinn's article are Conti, not Challenge), and Enve has had a beef with Challenge, as discussed here on the forum (https://forums.thepaceline.net/showthread.php?t=235090&highlight=enve+rim). Some people are like, yeah, Challenge tires suck. On the other hand:

i feel like this is enve saying "oh hey, we may not catch every burr on our rims so be safe and don't use something that's somewhat more delicate -- let's blame the tires, not the rims..."

It would be nice if they would simply finish the edges of their rims off. They are the only rim I've recently seen with sharp edges. Rims like Boyd, Nox, and FSE are all finished of with much higher quality.

I'm not doing carbon It would be nice if they would simply finish the edges of their rims off. They are the only rim I've recently seen with sharp edges. Rims like Boyd, Nox, and FSE are all finished of with much higher quality.

No personal dog in the fight for me.

[Hindmost]

If I understood the article correctly, it wasn't so much blow off as sidewall failure.

[R3awak3n]

I have had that exactly rim setup tubeless for a bout 1500 miles and has been great but now it has got me second guessing. Not sure his exact pressures but 6.5 bar is 95 PSI, that is WAY too much for tubeless. A lot of manufacturers don't recommend over 60PSI and it kind of makes sense.

[saab2000]

I've never had this happen but a buddy had a tire just the other day blow off a rim. I'll have to get details. It was a tubeless tire and his initial impression was a cut of the cords in the bead. Hooked, aluminum rim. He's not on this forum (or any other) but it extremely detail-oriented.

Personally, my only tubeless experience is with Pacenti SL25 rims and the Panaracer Gravel King 38mm herringbone tread tires. I use Finish Line sealant and run them around 40-42 PSI. This is a hooked rim. Initially I think I set them up with around 50-60 PSI and thought this absurdly low because I'm a roadie and think higher must be better but I know better because I run my 23s on wide road rims as low as 85-90 and 25s as low as 75-80 and love them and I'm no waif. This pressure was far too high.

The 38s at 40ish seem just right in terms of ride quality but I wish the rim were wider. Very small changes in pressure seem to affect ride quality or handling quality quite a bit more than these single PSI changes in narrow tires on narrow rims.

Anyway, it's not about all this but the other factors in the equation and safety. The hookless vs hooked rim is interesting and the linked article (and further links) about tire shape are very interesting and mesh with my own experience than wider is better when it comes to the resulting tire shape.

The folks I've talked to about hookless see no safety compromise as long as pressures stay reasonable and since my own experience with 40-42 PSI is good I'd say this is accurate. I'm experimenting with wider tires and lower pressures and will be trying some hookless rims in the spring. It seems even the rigidity of the casing is important.

Safety is always the primary concern and until now tires blowing off a rim has been an extreme rarity. I guess the tubeless thing brings its own real challenges. It seems to be documented more and more of late. That is disturbing.

[pbarry]

We should all inspect for Burrs. They are a dangerous lot.

[berserk87]

If I understood the article correctly, it wasn't so much blow off as sidewall failure.

That's the most significant point that I took from the article. He states:

"I think tubeless is a red herring here. I believe what happened to you could have also happened with a lightweight clincher tire with an inner tube. It sounds like the rim’s bead hooks cut enough of the threads in your tire casing that it blew."

And a nod to "pbarry" for one doggone fine historical reference!

[dddd]

The article quoted the tire guy mentioning a "Shafer's strip", which I had always read as a chafer strip, so hopefully this may be clarified.

Tires without the durable protective cloth strip over the bead area can have the casing threads severed or weakened by the sliding of even a plastic tire iron, so can be a source of this sort of blow-out.
Even the tires with thick rubber over the bead area can have some length this rubber sheared right off and the threads damaged at the same time, just by the sliding of the lever OR the pulling-off of the partially-freed tire!

The edge of even an alloy rim can pinch and "scissors" the threads as the partially-dislodged tire bead is pulled free of the rim, so I use caution not to exacerbate this tendency when dealing with a tire bead that needs force to fully remove.

[Clancy]

If I understood the article correctly, it wasn't so much blow off as sidewall failure.

My takeaway as well but also the sidewall failure was caused by a sawing action from the carbon rim, or so Zenn theorizes.

[yinzerniner]

We should all inspect for Burrs. They are a dangerous lot.

Only when in Weehawken at dawn!

But for real, take a look at this latest screed from Enve. A whole lot of marketing mumbo-jumbo and blame-shifting b.s. IMO.
https://www.enve.com/en/journal/behind-the-product-the-hookless-bead-how-it-works-and-who-theyre-for/

[RobJ]

Only when in Weehawken at dawn!



But for real, take a look at this latest screed from Enve. A whole lot of marketing mumbo-jumbo and blame-shifting b.s. IMO.

https://www.enve.com/en/journal/behind-the-product-the-hookless-bead-how-it-works-and-who-theyre-for/


Seriously? Where are they blame shifting? Seems to me like a lot of common sense explanation on rim/tire design and the ins and outs of proper tubeless. Since Enve has both hookless and hooked rims they’re not pushing any one agenda plus other manufacturers have hookless, so it’s not unique to Enve.

Looking for new wheels I have read a ton of the manufacturers tech info and I don’t see any of this as marketing. More people should read these type of things and be better informed so they don’t go running around placing blame for their own mistakes.

A major sidewall cut is not “a tubeless blowout”. Sensationalism. Just like the hocus pocus with latex tubes originally.


Sent from my iPad using Tapatalk

[colker]

Tubeless is worth the risk and pita on mountain biking. If you ride in cactus country there is no other way... On a road bike i will go w/ tubular before tubeless.

[9tubes]

Seriously? Where are they blame shifting? Seems to me like a lot of common sense explanation on rim/tire design and the ins and outs of proper tubeless. Since Enve has both hookless and hooked rims they’re not pushing any one agenda plus other manufacturers have hookless, so it’s not unique to Enve.

Looking for new wheels I have read a ton of the manufacturers tech info and I don’t see any of this as marketing. More people should read these type of things and be better informed so they don’t go running around placing blame for their own mistakes.

A major sidewall cut is not “a tubeless blowout”. Sensationalism. Just like the hocus pocus with latex tubes originally.


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Last winter there was a kerfuffle in the industry when riders were having catastrophic failures with the bead being cut. Enve rims were involved and that company issued a press release that blamed the tire manufacturers for poor tires. The tire manufacturers noted that the problem didn't occur on non-Enve rims. Challenge examined recent Enve rims and said there was a sharp moulding flashing on the bead, and the bead was not built to ERTO standards. Challenge and Vittoria recommended not using Enve rims with any tire. This seems to be a problem only with late-2018 and 2019 rims.

Since Enve didn't see it as their problem I don't expect a change but I don't have the most recent info on this.

www.bicycleretailer.com/product-tech/2019/03/15/tire-makers-react-after-enve-issues-warning#.XYp_8i-ZN-U

https://forums.roadbikereview.com/wheels-tires/enve-ses-wheels-consumer-safety-bulletin-367481.html

[Davist]

the recommended tire pressure chart is interesting, down to 46psi (180lb me) for 28s on gravel. I run low pressure (mostly 75 rear 65 front) on my 28s but this seems like rim damage levels (IF you weigh 90lbs it's 26psi!) https://www.enve.com/en/tirepressure/

[kingpin75s]

the recommended tire pressure chart is interesting, down to 46psi (180lb me) for 28s on gravel. I run low pressure (mostly 75 rear 65 front) on my 28s but this seems like rim damage levels (IF you weigh 90lbs it's 26psi!) https://www.enve.com/en/tirepressure/

Chart looks ok to me. I weigh 140lbs and tend to run my 35c tires at 35psi on gravel. Chart matches my experience well. YMMV and all that.

[saab2000]

Chart looks ok to me. I weigh 140lbs and tend to run my 35c tires at 35psi on gravel. Chart matches my experience well. YMMV and all that.

I also run far lower pressures than I thought reasonable or possible. The results are generally positive though it seems to be pressure sensitive. In other words, just a few PSI higher and the benefits disappear. Same with lower. The sweet spot seems narrow.

[Jaybee]

I also run far lower pressures than I thought reasonable or possible. The results are generally positive though it seems to be pressure sensitive. In other words, just a few PSI higher and the benefits disappear. Same with lower. The sweet spot seems narrow.

To expound on this, the wider the tire, the more sensitive the pressure range is. Your 25s may have a happy range of 3-5 psi, you might feel 1-2psi difference on your 40s, and on fat bike tires maybe as small as 0.25 psi is the difference between flotation and cutting through the snow crust.

[saab2000]

To expound on this, the wider the tire, the more sensitive the pressure range is. Your 25s may have a happy range of 3-5 psi, you might feel 1-2psi difference on your 40s, and on fat bike tires maybe as small as 0.25 psi is the difference between flotation and cutting through the snow crust.

I have found this to be accurate. When I was riding 22/23mm tubulars I wasn't super sensitive to this - I just pumped them up to 95 PSI or so and loved the experience.

Today I'm using 25mm clinchers with wide (20mm internal width) rims and have run them as low as in the 60s PSI. This is a touch low but not extreme. Yesterday's spin was quite comfortable but the front was a bit squishy. I later discovered it was in the low 60s. I used a frame pump and my finger tips to determine pressure. Not an accurate method apparently!

But the ride was good and didn't feel slow. Today I'm going to use more, but only about 75 in the rear and 70 in the front. These are new Continental GP 5000 with an inner tube on Boyd Altamont Lite rims.

[Mark McM]

To expound on this, the wider the tire, the more sensitive the pressure range is. Your 25s may have a happy range of 3-5 psi, you might feel 1-2psi difference on your 40s, and on fat bike tires maybe as small as 0.25 psi is the difference between flotation and cutting through the snow crust.

But isn't just a numbers game? Surely what matters is the relative (percent) difference, rather than the absolute numeric difference. A 2 psi change in an 80 psi tire is the same 2.5% relative difference as a 0.25 psi change in a 10 psi tire.

[Clancy]

But isn't just a numbers game? Surely what matters is the relative (percent) difference, rather than the absolute numeric difference. A 2 psi change in an 80 psi tire is the same 2.5% relative difference as a 0.25 psi change in a 10 psi tire.

My head hurts when I try to wrap it around this concept. Would someone please explain the physics involved to a simpleton like me?

Specifically I do not understand how a 25c tire requires 75psi while a 4 inch fat tire requires 10psi.

[benc]

Funny to me that there are so many tubeless skeptics out there. I'd wager the tubeless failure stats are not out of line with tubular and clincher failures. Things break, sidewalls blow, beads fail, glue fails, whatever...

I switched to tubeless road in 2012 and haven't looked back. I've run 95psi on 23c when i weighed 195 and now 70 psi at 175. 25k miles maybe with no memorable issues?

This is my actual wheel and tire in this video: https://www.youtube.com/watch?v=OBUfERZzHTM

That's me!

https://youtu.be/OBUfERZzHTM?t=301

[Hindmost]

My head hurts when I try to wrap it around this concept. Would someone please explain the physics involved to a simpleton like me?

Specifically I do not understand how a 25c tire requires 75psi while a 4 inch fat tire requires 10psi.

pv=nrt

[Mark McM]

Funny to me that there are so many tubeless skeptics out there. I'd wager the tubeless failure stats are not out of line with tubular and clincher failures. Things break, sidewalls blow, beads fail, glue fails, whatever...

That's not a particularly strong endorsement. Why use a technology that requires more time and trouble to set up and maintain, if it has the same failure rate as the technology it replaces?

In the latest Marginal Gains Podcast (https://marginalgainspodcast.cc/), Silca founder, former Zipp engineer and bicycle industry technical consultant Josh Poertner explained why he had returned to standard clincher tire and tubes after using tubeless tires. He said that time and effort to do clean up when switching tires made tubeless tires not worth the effort (and he said that the mechanics on the professional racing teams he works with had similar opinions). He also remarked on the tire rolling resistance tests he had done, which showed that tubeless tires had no RR advantage over latex tubes. For a guy who is all about marginal gains, this says something about how small the marginal gains of tubeless tires must be.

[Mark McM]

pv=nrt

I think you mean F=PxA (i.e., to support the same load (F)orce, a tire with a larger ground contact (A)rea requires less pneumatic (P)ressure );

[Jaybee]

But isn't just a numbers game? Surely what matters is the relative (percent) difference, rather than the absolute numeric difference. A 2 psi change in an 80 psi tire is the same 2.5% relative difference as a 0.25 psi change in a 10 psi tire.

My head hurts when I try to wrap it around this concept. Would someone please explain the physics involved to a simpleton like me?

Specifically I do not understand how a 25c tire requires 75psi while a 4 inch fat tire requires 10psi.

At the risk of pedantry, 10 psi in a 4" tire makes it a basketball. 7.5 on dirt/rocks for me, 3-4 for soft sand, 1.5-2 for snow.

I think Mark is probably right that the percentage changes for a given tire size are within a narrow range.

[9tubes]

My head hurts when I try to wrap it around this concept. Would someone please explain the physics involved to a simpleton like me?

Specifically I do not understand how a 25c tire requires 75psi while a 4 inch fat tire requires 10psi.

In layman's language, it's just that the number is in pounds per square inch and a 4 inch wide tire has more inches, thus the total is higher.

Example: if you held a postage stamp in your hand and we applied 1 psi to it, the pressure against your hand would be less than a pound. If we took a sheet of 8.5 x 11 paper and did the same thing, your arm would have to resist 93.5 pounds (that's 8.5 inches x 11 inches x 1 lb/in). If a windstorm applied one psi to the front door of your house it would be like an elephant sitting on it and would blow the door off its hinges.

The amount of force lifting your hubs up follows the same principle. It's a function of the cross section of the tire multiplied by the psi. Bigger tires need fewer psi to hold up the hubs.

[Clancy]

In layman's language, it's just that the number is in pounds per square inch and a 4 inch wide tire has more inches, thus the total is higher.

Example: if you held a postage stamp in your hand and we applied 1 psi to it, the pressure against your hand would be less than a pound. If we took a sheet of 8.5 x 11 paper and did the same thing, your arm would have to resist 93.5 pounds (that's 8.5 inches x 11 inches x 1 lb/in). If a windstorm applied one psi to the front door of your house it would be like an elephant sitting on it and would blow the door off its hinges.

The amount of force lifting your hubs up follows the same principle. It's a function of the cross section of the tire multiplied by the psi. Bigger tires need fewer psi to hold up the hubs.

Now that my simple mind can understand, physics for dummies! Thanks

[benb]

That's not a particularly strong endorsement. Why use a technology that requires more time and trouble to set up and maintain, if it has the same failure rate as the technology it replaces?

In the latest Marginal Gains Podcast (https://marginalgainspodcast.cc/), Silca founder, former Zipp engineer and bicycle industry technical consultant Josh Poertner explained why he had returned to standard clincher tire and tubes after using tubeless tires. He said that time and effort to do clean up when switching tires made tubeless tires not worth the effort (and he said that the mechanics on the professional racing teams he works with had similar opinions). He also remarked on the tire rolling resistance tests he had done, which showed that tubeless tires had no RR advantage over latex tubes. For a guy who is all about marginal gains, this says something about how small the marginal gains of tubeless tires must be.

This X1000

Even Carbon wheels themselves are marginal gains for everyone except the pros. They're marginal if your position isn't great. They're marginal if you're not really fast. They're marginal if you ride in a draft a lot of the time. A lot of the time if the pros are off the clock it sounds like they'd tell you the wheels are just marginal sometimes. Tubeless RR vs tubed often sounds like a joke too cause the differences in different tires/setups can be single digit watts.

Given all that and the high prices someone like Enve charges for their product they better be perfect and not have anything like sharp edges in the bead.

These products cost an absolute ton and do relatively little for anything except bling factor... any compromise in safety or any extra PITA for maintenance is not worth for me personally.

[tomato coupe]

Interesting article on yet another tubeless tire blow-off. But Zenn theorizes ...

... or so Zenn theorizes.

Zinn.

[yinzerniner]

This X1000

Even Carbon wheels themselves are marginal gains for everyone except the pros. They're marginal if your position isn't great. They're marginal if you're not really fast. They're marginal if you ride in a draft a lot of the time. A lot of the time if the pros are off the clock it sounds like they'd tell you the wheels are just marginal sometimes. Tubeless RR vs tubed often sounds like a joke too cause the differences in different tires/setups can be single digit watts.

Given all that and the high prices someone like Enve charges for their product they better be perfect and not have anything like sharp edges in the bead.

These products cost an absolute ton and do relatively little for anything except bling factor... any compromise in safety or any extra PITA for maintenance is not worth for me personally.

To be fair, wheels really aren't marginal gains since besides the rider they're the biggest factor when it comes to limiting wind resistance, which is the biggest factor for speed above 15mph. Going from even decent shallow to medium depth often increases speed 5-10% for the same effort, which is not a marginal gain - it's an easily measurable and observable one.

And as for overall ride feel, wheels again are second only to tires in improving grip, comfort, and handling.

Yes, a decent set of fast carbon will set you back $1000-3000m whereas improving riding position is free and a new set of tires costs $150 max. Whether the investment is worth the improvement is up to the rider themselves.

But it all depends on the priorities of the rider. If they're looking for as little maintenance as possible while attaining an adequate level of riding enjoyment, then more time-tested methods are probably preferred. But for riders who value absolute speed (most), technology (some), or bling(none admit, but all secretly do) the allure of deep carbon wheels is intoxicating.

[bigbill]

This post reminds me to look at the two tubes in my saddle bag to make sure they aren't dry rotted. They've been in there 2+ years since I switched to tubeless.

[Mark McM]

To be fair, wheels really aren't marginal gains since besides the rider they're the biggest factor when it comes to limiting wind resistance, which is the biggest factor for speed above 15mph. Going from even decent shallow to medium depth often increases speed 5-10% for the same effort, which is not a marginal gain - it's an easily measurable and observable one.

For those kinds of speed changes, you'll need to be using wheels with negative drag, that actually propel the rider forward. The drag of the wheels is typically only about 10% of the total drag. And because drag power increases with the cube of speed, even if the drag of the wheels was reduced to zero (and no aerowheel is even close to that good), it could only increase by speed by 3.5%.

Actual measurements show that the very best aero wheels (dual disc wheels) can increase speed by about 2% over box section wheels (at a nominal speed of about 25 mph). But most deep section wheels provide less drag reduction than that, so a speed increase of more like 1% or less should be expected. A 1% speed increase at a nominal 25 mph is only 0.25 mph, and that's at steady speeds on flat roads. For most riders, that kind of gain is quite marginal.

Also, while it is true that majority of drag on a bicycle is wind resistance, the vast majority is the wind resistance of the rider. The next highest drag is tire rolling resistance, which can be larger than the air resistance of the entire bike combined (wheels, frame, and components). It is cheaper and easier to get speed gains by switching tires than by switching wheels.

[yinzerniner]

For those kinds of speed changes, you'll need to be using wheels with negative drag, that actually propel the rider forward. The drag of the wheels is typically only about 10% of the total drag. And because drag power increases with the cube of speed, even if the drag of the wheels was reduced to zero (and no aerowheel is even close to that good), it could only increase by speed by 3.5%.

Actual measurements show that the very best aero wheels (dual disc wheels) can increase speed by about 2% over box section wheels (at a nominal speed of about 25 mph). But most deep section wheels provide less drag reduction than that, so a speed increase of more like 1% or less should be expected. A 1% speed increase at a nominal 25 mph is only 0.25 mph, and that's at steady speeds on flat roads. For most riders, that kind of gain is quite marginal.

Also, while it is true that majority of drag on a bicycle is wind resistance, the vast majority is the wind resistance of the rider. The next highest drag is tire rolling resistance, which can be larger than the air resistance of the entire bike combined (wheels, frame, and components). It is cheaper and easier to get speed gains by switching tires than by switching wheels.

I think your math is off once again.
When you cited your numbers, I'm guessing you used this study summation, to wit the operable numbers are:
The total drag of the wheels is in the range of 10% to 15% of the total drag on a bike. Drag improvements between wheels can reduce this by 25%, or 2% to 3% of the total drag.
https://analyticcycling.com/WheelsConcept_Disc.html

However if you go to this study they summarize that the difference in speed is between 3.7-9%, and they just tested 25mm wheels vs 50mm wheels:
The time trial simulation shows an advantage of the Vision
wheelset (Table 1). The cyclist needs 3.7% and 9.0% less time racing with the Vision wheels than with the Campagnolo and Bontrager wheels, respectively, with the assumptions done.
https://pdfs.semanticscholar.org/8843/ee7e05f3ba420c9ee717c831bd5049996f39.pdf

Granted this is at time-trial speeds so the gains for commonfolk will probably be less, but it still shows that wheels can make a measurable difference not just a marginal one.

But agree wholeheartedly that the biggest gains are rider and rubber.

[Mark McM]

I think your math is off once again.

Please show the error in the math.


When you cited your numbers, I'm guessing you used this study summation, to wit the operable numbers are:

https://analyticcycling.com/WheelsConcept_Disc.html

However if you go to this study they summarize that the difference in speed is between 3.7-9%, and they just tested 25mm wheels vs 50mm wheels:

https://pdfs.semanticscholar.org/8843/ee7e05f3ba420c9ee717c831bd5049996f39.pdf

Granted this is at time-trial speeds so the gains for commonfolk will probably be less, but it still shows that wheels can make a measurable difference not just a marginal one.

I'm not sure that you should base your argument on one study. Especially a flawed study, like the one you posted. The study used riders riding on rollers in a wind tunnel. At first glance, this may appear to be a better model of the real world than testing wheels/bikes alone. But other researchers have found that it can be very difficult for a rider to duplicate their exact position, run after run, so using live riders tends to produce erratic results. In addition, since the aero drag of the wheels is just a small portion of the total drag, it reduces the measurement sensitivity of the variable to be measured. Due to combination of the small influence of the wheels, and the large variance in uncontrolled variables, you can potentially introduce measurement errors in the same magnitude of the variable to be measured.

The study first makes this statement in regard to the contribution of wheels to aerodynamic drag:

Three forces contribute to the total drag: drag of the rider and any streamlined apparel, drag of the bicycle frame and drag of the wheels. The first contribution is the dominant one but it is extremely difficult to determine accurately and consistently. Rider’s drag is about 60–70% of the total drag depending on the position [3,4]. The contribution of the wheels is from 10% to 15% [5] while, considering the whole bicycle (frame and wheels), it is about 31–39% of the total depending on rider’s position and wheels [1].

But the graphs of the data show contradictions to these statements. In the graphs of CdA (which is proportional to aerodynamic drag), they show changes of up to 17% between wheels (a reduction in CdA from 0.29 m^2 to 24 m^2). That is an unreasonable reduction in aerodynamic drag, more than then the 15% total wheel drag the authors originally stated. The authors present no explanation of how changing between wheels can reduce total drag by more than total drag of the wheels.

According to the paper, the two aero wheels tested can decrease the time on a race course by 3.7% to 9% over a more traditional wheel, or a difference of 5.3% from one aero wheel to the other. In the recent Time Trial World Championship, 5.3% was the time difference between 1st and 15th place. If the conclusions of the paper is correct, then if different wheels had been selected by competitors, 15th place finisher Dylan Van Barles could now be the World Time Trial Champion.

The authors of this paper are the not the first to attempt to quantify performance improvements based on wind tunnel data. But most found that aero wheels provided more modest improvements. For example:

https://www.cyclist.co.uk/in-depth/1467/aero-rims-vs-lightweight-rims

‘At 40kmh, the switch from shallow rims to deep sections could be worth around 10W, which could save you 30 seconds over the hour,’ says Rob Kitching, founder of performance-modelling outfit Cycling Power Lab.

When Flo Cycling did modeling based on wind tunnel data of their wheels (https://flocycling.com/pages/aerodynamics), they found that their best wheels (solid disks) saved 1' 14"" in a 40K TT (about 2%).

The time savings estimates in these examples are more in line with both independent testing of aero wheels, and with the data offered by aero wheel manufacturers.

[benb]

If you're riding in a relatively upright position on the hoods & you aren't averaging 25mph then you don't need to get through Mark's math.

You're riding them for bling.