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12 May 2015

Road bike tire review: Bontrager R3 700x25 clincher (but, is it really 25mm wide?!)

I recently purchased a Bontrager R3 700x25 tire, moving up in width from Bontrager R3 700x23. The main reason was that I was looking for more comfort, for my 100kg weight. The 23mm width felt too sensitive to shocks and road vibrations, so much, that I was feeling as if I was slowing down instead of going faster. The 25mm width seemed logical to compensate this problem.

I have been using the R3 700x23 for about 18 months, with only 1 puncture (rear tire) and that was due to my fault hitting hard inside a road hole. Compared to R2, the R3, feels 'softer', faster, more responsive. I wanted a 25mm wide tire though, to give me some extra comfort.

I normally inflate the front R3 with 105-108psi and the rear R3 with 112-115. Sometimes, I might take 2-3 psi away from both tires to boost comfort, but I can observe a noticable reduction in top speed and acceleration.

On my new R3 700x25 setup, I did this test: Front wheel remained at 700x23, rear R3 wheel now gone from 700x23 to 700x25. Upon inflating both tires at the same pressure (115psi) for testing purposes: To measure tire width in order to double check manufacturers specifications. I noticed something weird, which I didn't see before in any tire: To my surprise my findings were the following:
Front tire width: 23.6mm (instead of 23mm)
Rear tire width: 24.3mm (instead of 25mm)


The tires were mounted on Pro Lite Bracciano A42 (alu, clincher) wheelset.

"What's is going on over here?" I thought. I wanted to gain some extra 2mm on the rear wheel and instead the width was 0.7 off the stated value. And not only this: The difference in width between the 23 and 25 tires was actually 0.7mm, far away from the expected 2mm! So, I didn't gain much, did I?

I will keep this post updated and I will add some extra photos of my measurements soon.. My current explanation for this 'unusual' measuring paradox may have been caused by one or a combination of the following issues:
  • The width of the rim affects tire width too. A given tire, measures narrower on a narrower rim and wider on a wider rim. When Bontrager states that this tire is 700x25, we also need to know the width of the rim it used to reference this number.
  • The front tire was about 2,000km 'old', while the rear tire was new. New tires can slightly 'stretch' or 'deform' with the use. So, at the moment, I leave on the side the above measurements until I ride a few 100's of km on them to see whether this is true or not.
  • Tire width specification is 'sometimes purposely' different from the actual value, in an attempt to keep tire weight lower than the competitors' tire of identical stated dimensions. That is: Company A produces 700x25, but in reality it measures 700x24, while Company B produces 700x25 and it is indeed 700x25. But, the tire of Company A is now lighter than the tire of Company B. So, customers go for tire of Company A as it is lighter, despite the inaccurate tire width!
I really don't know what the real problem is here. I will write more around this issue as I ride the new R3 700x23 700x25 combination.

The bottom line is that R3s are generally very good tires, both for training and racing too. I have only tested them in dry hot conditions (like those found here in Greece!), otherwise I don't know their behaviour in wet conditions. Puncture protection seems good: I am 100kg, but surprisingly, I feel 'safe' in terms of flats with these tires. They corner well too. Compared to R2, R3 have a very noticeable advantage both in terms of top speed and rolling resistance. I've noticed that these tires need to be inflated towards their higher psi range (90-125), that is, they are pretty slow when you inflate anything below 105psi or so. So, if you're up for some good speed go for 110psi at least. You might be ok, with 110psi at rear wheel and 105psi at front wheel, but do this only if you have some very specific reasons, e.g. more comfort in bad roads, and you don't mind too much about speed. For top speed I inflate both tires at 115psi.

Measurements (all tires clincher, at 115psi on Bracciano A42 wheels)





1 comment:

LostTime said...

I just purchased the identical tire on A9 Bontrager rims.

I glanced at you comments and you certainly did a lot of work.

The thing is these numbers - 25mm etc are technically 'nominal' values, a tire is not a precision item and the accuracy/precision of the manufacturing process is below the tolerances of the measuring device.

I am actually suprised they are even this close to 25 mm, the range could be a big as +/- 20 percent of nominal declared numbers.

Things such a vitamin claims in cereals are the same - these are mean claims with large CSV ranges, it just sstatistics.

Fact is a 25 is bigger than a 23.

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