Tomm Willians

Do bike tire manufacturers give a top speed rating for their tires? I recently watched a video where a cyclist claimed (and it looked pretty real) that he was doing 65mph on a steep decline. And concerning wheel manufacturing as well, are there limits beyond self preservation?

mstateglfr 

I have never seen nor heard of a tire speed rating. A bike tire is totally different from a car tire in width, composition, and load management.
I have never seen nor heard of a wheel speed rating. If a hub cant safely spin fast, thats just a POS bike component.

70sSanO

I think the bicycle speed record is over 180mph.

John

Edit added: Bicycle tires were not used to set the speed record. Small motorcycle rims and drag tires were used. There was a statement in the video that bicycle tires would explode at those speeds. Not sure of the science behind that, but an interesting video.

indyfabz

I hit close to 50 mph on a fully loaded touring bike. I don't think there is anything to worry about.

Rolla

I think some tires designed for e-bike use are speed rated.

Broctoon

I suspect that all mass produced bike tires are designed to withstand speeds in excess of what you'll ever encounter in regular use, i.e., 60 mph or so. Special cases, like the speed records set under very abnormal conditions (drafting behind a vehicle, using extremely large chain ring and/or compound drive train, running on a dry lake bed or salt flats, etc.) would be an entirely different situation. On a regular bike, even flying down a steep hill--say 12% grade--and getting as aero as most of us could ever hope for, I think you'll reach a terminal velocity somewhere around 60 to 70 MPH. That's just my guess. Presumably, bike tires are expected to hold up to that speed plus a bit more for a safety margin, so there's no need to publish speed ratings or mark them on the tire.

alcjphil

I remember years ago watching a stage of the Tour de France during which Thor Hushovd won 2 mountain stages. He was World Champion that year and on his way to winning the green jersey. On one of the high mountain stages he attacked early on the last big climb from a breakaway group. He was caught and passed close to the top but managed to catch up during the approach to the finish. Thor was one of the best descenders ever, his team manager, described his bike handling as "otherworldly" Apparently he hit speeds of over 110 KPH on the descent. He was so fast that there was no coverage because the following motorcycles couldn't keep up and the only part we saw was close to the finish on the flat run in where the motos were able to catch up
His other mountain stage win was also memorable, finishing in a 3 man sprint which I always think of as the "Norwegian sprint"

https://www.newsinenglish.no/2011/07...-cycling-hero/

rsbob 

Shortest thread ever?

Iride01 

How often do you yourself hit 65 mph on a bike?

bbbean 

Descending riders routinely push 60 mph on a variety of tires. If you crash at high speed it is MUCH more likely you crashed because of handling, road conditions, or human error. Consider the fact that bike tires don't change temperature as much as auto tires, due in part to the fact that they aren't carrying much load or much force.

63rickert

Normal bike, normal tires, special rider. He did this a number of times for journalists and does not seem the least bit stressed. If you don't care to follow link it shows Theo Bos drafting at 140kph. About 86mph.

LarrySellerz

I recently got a gatorskin on my back tire and it started to feel weird on the first big descent (prob 35-40 mph) enough so that I stopped to examine the wheel.

rsbob 

Have never heard of a high speed tire failure due to exceeding the tires’ threshold on a bicycle. I am sure there have been defective tires which have given out at speed. Could see an under inflated tire on a tandem ridden at speed having a sidewall issue, but under inflation is not the tire’s fault.

tcs

The other component is time. How long is a cyclist going to spend going 110kph? A few minutes at most? Unlikely a tire carcass is going to degrade in such a short time.

Mtracer

Here's my effort to put some numbers on this. I could certainly have made a mistake, so don't anyone take these as fact.

Seems like there are two possible failure modes; excess rotational forces and excess heat. Here's some back-of-the-envelope calculations.

Heat would come mostly from rolling resistance. From the Bicycle Rolling Resistance website, it appears most road tires are in the range of <15 W at their test condition of 8 m/s. This will increase as the square of speed. So, at say 30 m/s (~ 60 MPH), this would be about 210 W. That's certainly a non-trivial amount of power. But that much power spread over the surface area of a tire would seem unlikely to raise the temperature that much. Certainly not enough to cause the tire to fail. Even less so when you factor in that heat will also be conducted to the rim. And of course there is a huge amount of airflow cooling the tire due to the high descending speed.

So, I don't think the tire will overheat and therefore I don't think it would matter how long the descent lasted.

High rotational forces could cause the tire to come off the rim, spokes to break or pull through the rim or hub, or similar failure. This would require a lot of calculations and material science analysis to figure out what speeds this would happen at. But it is possibe to get some idea of the forces involved and how they compare to nominal forces on a bike wheel.

It is easy to calculate the G-forces trying to pull the wheel apart.

Assuming a radius of 0.35 m (half a 700 c rim diameter) and a speed of 30 m/s the acceleration outwards is quite large at 2,571 m/s^2 which is about 260 Gs.

Some ballpark values for a tire and rim mass would be tire (200 g) and rim (500 g). Obviously these vary a lot. At 700 g total, the tire and rim mass are exerting about 1,800 N (~400 lbs). Assume 28 spokes, that's 14 lbs per spoke. While certainly significant, nominal spoke tension can be in the range of 100 kgf (~1,000 N = ~ 220 lbs). So, an additional 14 lbs of force per spoke is just a fraction of the nominal force on the spokes.

From this it seems there is no chance of a typical wheel failing from rotational forces at speeds around 60 MPH.

As for a tire coming off. Again assuming a tire mass of 200 g, the force on this is about 500 N (112 lbs). Given a rim circumference of about 87 inches, that's about 1.3 lbs of force per inch pulling out on the tire. For a rim that is about 1 inch in width, this would also be about 1.3 PSI of pressure. This is a fraction the pressure the tire is under normally. So, again, seems like no threat at all.

rollagain

If I got going at ~50mph on a bike, I'd worry a lot more about my brakes than I would about my tires.

KerryIrons

Nope. Heat generation (the reason automotive tires are speed rated) is caused by the number of flexes of the tread/casing. This increases linearly with speed, not with the square. Aero drag increases with the square of the speed and power to overcome aerodynamic resistance increases with the cube of the speed.

alcjphil

Excellent point. Tire flex generating heat is a real thing for car tires, but unless someone can find a -10%, 100km long downhill it isn't likely to cause problems for bicycle tires. I have hit 90 kph a couple of times on downhills, but never for more than at most 3-4 minutes. Actually, if I have to be honest, it more like 1-2 minutes at most, just seemed longer

Mtracer

Rolling resistance is actually, a combination of linear and non-linear processes. But I think you are correct that for a bike tire it is mostly linear over the speeds of interest. Which, makes it even less of an issue concerning potential tire heating.

KerryIrons

From a heat generation standpoint, the flexing of the casing and tread rubber is the source of any heat. The number of flexes is linear with speed. Please explain the non-linear aspects.

Mtracer

Online references show an increase in the coefficient of rolling resistance as speed increases. I'm not a tire expert, but simply put, I don't think there is a reason to assume the losses in flexing the tire are independent of how fast the tire flexes. Put another way, the losses are frequency dependent which is a perfectly reasonable expectation in any system.

What I assume is that the hysteresis losses increase the faster the tire flexes. Or perhaps it is due to a change in tire temperature affecting the losses as higher speeds increase heat.

Though again, these speeds are relatively high, and I agree do not seem to apply to bicycles. I.E., bicycle speeds are slow enough that a linear model is close enough.

Attilio

I have never heard of a speed rating for tires but if you go 65mph and something bad happens we only pray that the bad thing occurs before the cyclist can or does reproduce or if doesn't die then suffers permanent damage to otheir genitals such that reproduction becomes impossible so as to keep the human gene pool under best possible quality control.

Honestly anything more than 30 feels pretty fast. More than 40 is unreal can count on the fingers of one hand, usually in tunnels I didn't expect like in Italy on a downhill and was afraid so wanted to keep up with traffic and get out of there ASAP. My personal record is 45mph and was terrifying, I normally go out of my way to stay below 30 even on group rides.

DaveSSS 

I hit 50-57 mph on most of my regular routes. I'm using tubeless tires and hookless rims with 52/56 psi. Works fine. Brakes aren't used except for one descent that ends in a curve, so a few seconds of braking reduces my speed to around 40 in the curve.

rydabent

I remember that in an early attempt at a motor paced bike speed record, the bike tires flatted. The bike has Shrader valve stems and at speed the centrifugal force cause the valve stems to open.

Ironfish653

I've been at 160 mph on a 1100cc Superbike (moto). It had regular Shrader valves on it, too, but I did not experience any loss of air pressure.

I wonder how much faster that bicycle was going, to unseat the valve stems?