How many of us have done the old thumb test on our tyres before a ride, or even better (or so we may think) have got the track pump out and pumped up those tyres to 110 – 120 Psi before venturing out for the morning ride. Have you ever found yourself looking for new tyres and getting the 700×22 because the thinner tyres will go faster?
That’s what I have been doing, and I found out that this may be the wrong thing to do. I was recently looking for wheels on an overseas site and a friend pointed me to some tyres. Someone had done a review of the tyres and pointed to an interesting article that suggested we should not be pumping our tyres up so much, well at least we should not be having the same pressure in the front as the back. There was also the suggestion that those bigger guys (yeah at 85kg I qualify) should be riding wider tyres.
The article suggests that we (road cyclists) should look at what weight is carried at each tyre and adjust our pressure and tyre size to suit. An 80kg rider might be better off riding on 700×25 rather than 700×23 as there is less pressure required in the larger tyre to prevent excess tyre drop. So rather than having to pump up the tyre to 130psi to avoid a greater than 15% tyre drop, you only need to pump it to 100psi.
This assumes that the manufactures of tyres have what is called a recommended tyre drop percentage of 15%. That is that when inflated and the weight of the rider on the bike is applied, the rims should only move towards the ground, due to compression of the tyre, by a margin of 15%. I have asked a few tyre companies (Vittoria and Continental) whether they actually have a recommended tyre drop percentage and Vittoria have suggested the following table from their most recent catalogue for pressure, but not tyre drop. (I am trying to clarify further with Vittoria and will update when I know.)
Source – Vittoria
This table suggests that for differing compounds (tpi) you have different pressures both front and back, supporting the premise made regarding tyre drop. TPI (Threads Per Inch) is described as
“Lower TPI tyres have thicker cloth and the gaps between the threads are bigger. These take on more rubber as the tyre is made, making a heavier tyre but with sturdy, abrasion resistant sidewalls. A low TPI count is good for a downhill tyre.
Higher TPI tyres take less rubber to fill the gaps so give a lighter tyre with lower rolling resistance as a result of having more flexible (thinner) sidewalls. Also the smaller gaps between the threads make it harder for a thorn to penetrate the casing. For racing, touring, or any performance oriented tyre, a high TPI count is good.”
Source – http://www.moruyabicycles.com.au/contents/en-uk/d713.html
Vittoria also go on to suggest the following when determining the correct tyre pressure to run. They suggest to use a small criterium style circuit with varying types of corners. Start with the above pressures and each lap lower the pressure by 5psi until you start to feel the tyre “wallow”. This presure will be your low pressure point. Start again from the recommended and raise your tyre pressure each lap by 5psi until you start to bounce or skip across the surface. This is your high pressure point.
There are some issues with this, as I would not want my front tyre wallowing while cornering at the wrong speed, neither would I want it to skip as I was mid corner. This method is up to you if you want to follow it, but I recon just sticking with the recommended pressures would be good enough.
I received an email back from Conti regarding the question of tyre drop. The sales rep indicated that he had been working in the industry for 25 years and had never heard the term. He further recommended that you inflate tyres to the maximum pressure indicated on the side wall of their tyres. I guess everyone has a different view of tyre pressure.
The tyre drop article outlines a different view. We should be sitting our bikes on a set of scales. Put all the gear that you ride with on (ie if you commute then strap on the backpack for this exercise), then place the front tyre on a set of scales and hop on the bike, make sure you put something under the rear tyre so that you make it level. Record the weight on the front wheel. Then do the same for the back. Once complete look at the weight on the graph (and note that the weight is for the individual tyre not the whole bike) find your tyre size and inflate according to the tyre size that you have.
Breaking this down also allows us to adjust the width of our tyres from front to back, so having a 700×22 on the front and a 700×25 on the back and running pressures of 90psi/100psi may be the optimal set up for our handsome steeds (Did you here that Shrek, she called me a handsome steed. – Donkey from Shrek).
Conversely you can use the 40/60 rule for your weigh distribution. 40% of your total weight will be on the front wheel and 60% will be on the back (This only really applies to racers however). I have tested this theory out and with a total weigh (bike and body) of around 95kg + the 5kg bag that I carry to work, I figure that I have 60kg on the back tyre and 40kg on the front. After using the scales this measures up about right. But what does this say about my 700×23 on the back wheel. Looks like my next back tyre will have to be a 700×25 and I’ll have to pump it up to about 120psi. I think I might run a 700×22 on the front and run it at about 100psi. Thankfully I have a good floor pump, but that’s for another post.
So what size tyres do you ride on and what pressure do you run. Tell us in the comments.
Wow! Very comprehensive Jorgy. Funny, I wasn’t as researched as you. I just thought as more weigh on bum side – more air, less so on front. I run 320tpi 23, so my rears I pump to 120-125psi pre-ride and front about 115psi. I’m 86-87Kg. I think my rims are rated to 160psi but I dare not go past 130. Any thoughts about grip in the wet with 25s?
Raph, Vittoria indicated that you should decrease tyre pressure by 7.5psi for Clinchers and increase by the same amount for Tubulars. Bit strange but that’s what they said.
with my massive 83kgs, i ride at between 130-140 psi. Wonder why my bones always get rattled. Although i will soon be using less as new tyre max pressure is only 120 🙁
I read an article recently on this subject by Chris Carmichael (Lance Armstrong long time coach) and it was along similar lines. He gave an example of Levi Leipheimer’s tyre pressure were he races with his front tyre at 100 psi and his rear tyre at 110 psi. Interesting topic for discussion.
Very interesting…always knew tyre selection and good pressure as being important factor, plus I always drop pressure when wet….but never considered differing pressure for each tyre. Might give it a go. SPR think tank is alive & kicking. Can’t wait to hear Ainseys key findings on seat post-posterior ergonomics.
Great stuff. We all put a lot of effort into our riding and it is a good reminder that what ultimately transfers our effort into forward momentum is a thin bit of rubber.
One other consideration regarding tyre width is aerodynamics. Zipp (and others) have discussed at length the optimal tyre width combination for aero wheels. Below is a brief summary of their ideas:
Tire choice depends highly on user preference and conditions. To summarize, a 21mm has superior aerodynamics with our rims; a 23mm is larger and subsequently has better ride quality and rim protection, but at a slight aero penalty. Here are some questions you can ask that will help guide your decision:
Triathlon/Time trial? In general – 21mm.
Road racing? In general – 23mm.
Training and/or daily riding? 23mm+
Dry? 21mm at normal recommended pressure.
Wet? 23mm at a slightly lower pressure.
Smooth roads? 21mm at normal recommended pressure.
Rough roads? 23mm at a slightly lower pressure.
User prefers slight aero benefit of 21’s at the expense of a little ride comfort, rim protection, and rolling resistance? Use 21mm.
User prefers slightly better ride comfort, rim protection, and rolling resistance of 23’s at the expense of a little aero? Use 23mm.
Rider weighs less? 21mm.
Rider weighs more? 23mm.
I’ll drop my front to 100psi and rear 110-115 and see how it goes. Probably can’t tell the difference.
Hi Jorgy, not sure what the intent of your research was but tyre construction, size and pressure all impact ride comfort, rolling resistance and aerodynamics.
Have a read of this article:
http://tinyurl.com/2cvu5nv
Some interesting points here on hydroplaning.
For your interest, if you weren’t aware, continental ahve been flogging these for a few years now: http://tinyurl.com/yzpt29w
As for aerodynamics, you get most bang for your buck with an aero helmet. Try that on the Saturday bunch ride 😉
At the end of the day, at my level at least, I’d be better off training more than worrying about a few psi here or there.
FWIW: ~70kg, 700 x 23 at 100 – 120 psi depending upon the road surface.
Is anybody else running tubeless on their roady? I find them quite good and have had them running as low as 60psi with no sense of wallowing.
i pump mine to 130 for clinchers, and tubulars 150 front 160 rear, i run less in the front to help with courners
Sparticus ran 25mm zipp 303 tubulars with 80 psi front and 110 in the back at Roubaix,
@Chuck. Yeap have seen both of those. Interestingly the guy at Conti forwarded the link for Sheldon Brown’s site to me and I was about to link to it for everyone. Thanks for beating me to it.. 😛
The Conti tyre combo of Force and Attack was the catalyst for this “research”. Plus I was interested in the tyre pressure v width v weigh chart and thought you guys might be interested as well/get something out of it.
I know I’ll be changing from a 23 rear to a 25 and probably put a 22 or leave the 23 on the front.
I’m in the same boat re training. At my level, I am more worried about getting the training in, but I guess every little bit helps.
chuck – I had a go at running Hutchison fusion tubeless on my 2 way fit fulcrums, but found the tyres did not last long at all. Couple of weeks and they were cut to pieces. The ride quality was good, but tyre durability was below average (unless I just had a bad run?)
I have read a few forums that raised the same issue, good idea….just need the quality rubber to be introduced. What type are you using as I would consider trying again?
I tried the Force/Attack combo but found them too frail. I was fixing punctures every second week (both front & rear prone), and got sick of it after about 3 months of it. Had similar issues with GP4000 so I’m not having much confidence in Conti. Swap to Maxxis columbiere – they were good but grip in wet so-so and had 1 puncture in 12months riding in them. Now I’m trying Vittoria Corsa Evo CX, only because it advertises 320tpi. I like the ride of it but the tyre does get cut up easily. Having said this, I’ve only had 2 punctures (both rear) on it in 6 months.
Shane – I had the atom on my ultegra wheels. Probably done >1500km with no problems and on a par with any of the other high end tyres I’ve tried. I know you’re a sprinter not a climber 😉 so perhaps that has something to do with it?
They do seem to wear a little quicker than say a GP4000 but I’d expect that for a more performance oriented tyre.
If you want cut and puncture issues try the conti supersonics. 1000km if your lucky. Great grip while they last though.
Raphael – the corsa evo’s are race tyres and will cut up easily. Nice tyres, had them, love them. I know Jason C from the fast group uses these with minimal punctures.
If you want a great all round training tyre try the Conti GatorSkins. Three layers of puncture protection, ride fairly nice and will provide alot ‘hassle’ free km’s.
I’ve been on a set of these for almost 8 months without a puncture. Personally I prefer latex inners over butyl rubber as they provide greater comfort and are said to roll better, lighter and are less prone to punctures.
I read that during the TOC Michael Rodgers used a 25mm rear as it provided a great level of ride comfort as he had to the ability to run a lower PSI.
Listen to Chuck and go the supersonics with the latex tubes.. Lucky to get one ride with no punctures… 😉
I’ve run the GP4000 for nearly 12 months. Well over 2000km and not a single puncture. Due for replacement now – and I will go another pair without a second thought. Love em to bits.
Just put a new pair of Vittoria Rubino PRO Slicks on my track clinchers. I have the following to say – Vittorias are soooooo much easier to put on than Conti’s. That is all.