Slime vs normal tube

w7london

I just changed to slime on the rear wheel, and I *think* there's a lot more drag (I mean I'm doing more work than I used to) - but I'm not sure if that's just psychological!

Would I really be able to feel a difference?

I also changed to Smart Sam tyres a few weeks ago, so I guess that's adding to the weight.

My question is just: is my mind playing tricks, or should I just shut up and learn to love the slime?

singleton

Slime tubes will add more drag, but I'm not sure whether or not you will be able to feel the difference.

Have you adjusted anything else? Lowered tyre pressures?

w7london

Nope, still at 45psi

singleton

What size tyres are those? Since this is posted in the MTB forum, that sounds very high to me.
I run my road tyres about 70-90 PSI but my off-road ones about 20-25

steve_sordy

Slime tubes are heavier, much heavier. And you can tell when riding!

It's a long time since I even used tubes, let alone weighed them, which is why these figures are for 26" tubes.

Plain, presta valved inner tubes 26” (1.75 – 2.125) weigh 192g .
Similar 26” (1.9 - 2.125) weigh 160g

Ie inner tubes can vary in weight quite a bit.

The Slime, inner tubes that I bought weighed 315g each, ie 123g - 155g extra weight per plain tube.

Scale that up for a 29er and you get 137g - 173g extra weight.

Don't forget that weight is in the tyre, right where you can feel it the most. Weight at the wheel not only has to be accelerated horizontally, but rotationally as well. That extra resistance you feel is you having to provide extra power to overcome the extra rolling moment of inertia of a heavier wheel. It's a lonnnng time since I did that sort of maths, but I'm fairly sure that the effect goes up with the square of the diameter.

You will feel it every time you try to accelerate or slow down, and when you are trying to change direction, especially when doing quick left - right - lefts.

If you were to go tubeless, you would replace that Slime tube with maybe 80-100gms of sealant, depending upon tyre size.

steve_sordy

I agree with @singleton 45 psi seems very high. In full kit I weigh 92kg. On 27.5 x 2.2 tyres I had 22 in the front and 24 in the rear, tubeless.

w7london

Thanks all, this is really useful info.

I ride an MTB but mainly on road (I know, I know!) so I keep the pressure at the high end. I'm using Smart Sams which I think are rated at around 30-54psi.

They're 27.5 wheels.

w7london

The reason I'm using Slime (and Smart Sams) is out of desperation. I got 8 punctures in a month - changed to Smart Sam with normal tubes. Got another puncture a few weeks later and thought, right, going over to Slime now.

But yeah I think I feel a weight diff (and i only have Slime on the back wheel). I'm not sure whether to stick with it or go back to normal tubes.

singleton

Somethings wrong.
I've ridden over 5,000 km in the past 12 months on the road, in all weathers and all conditions, with road tyres, with non-slime tubes and I've not had a puncture. Now maybe I've got a bit lucky, but you shouldn't be getting that many.

But if you want fast tyres for riding a 27.5" wheel on the road only then you may want to consider some slicks. There's a lot of 27.5" / 650b slicks coming out now as the number of gravel bikes and adventure bikes are increasing.

w7london

@singleton what do you think is going wrong?

joe_totale-2

8 punctures in a month either suggests that you ride over glass all the time or each time you get a puncture you're not checking to find out what caused it and left the culprit in the tyre ready to cause another puncture.

No way should they be happening that frequently.

w7london

@joe_totale-2 not checking the inside of the tyre was definitely responsible for at least 3 or 4 of those punctures!

But the rest of them, I'm not sure about. I even went to extreme lengths of changing both the tyres and tubes at the same time to make sure everything was fresh and undamaged (and I checked the wheel rim too). Which is why the next puncture (about 3 weeks in to the new set) was so disappointing.

The latest puncture was a pointy stone that went straight through the rear tyre.

I think I'm quite careful about not riding over dirt on the side of the road/avoiding glass. But i don't know.

singleton

Some years ago I have several punctures in quick succession, and every time I checked the inside of the tyre. First time was a bit of a quick check, but I then started checking more carefully. I eventually found a small piece of flint deeply embedded in the tyre.

Maybe it's the above, maybe rim tape has moved and a spoke or sharp end is poking through.

I won't ask if your tyre pressures are too low as we've already established that they are in fact quite high.

You know the reason for latest puncture - a pointy stone - but it's important to try to find the reason for every puncture. Like my experience with the flint, if you can't find the reason, then you can't be sure it won't just happen again.