Things to check when renting a disc bike

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biwa
Posts: 161
Joined: Fri Sep 21, 2018 8:39 pm

by biwa

Going to ride in mountains with a rented disc bike, just wondering what checks I need to do to make sure it's safe and sound. Never ridden a disc bike before and this one has di2 too (also new to me). Thanks!

by Weenie


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Lewn777
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by Lewn777

-Do a visual check and make sure there are no fluid leaks around the calipers, cables or levers.

-Check the levers, they should feel firm when pulled and both similar and not mushy.

-Lift the rear off the ground and give the wheel a spin check for exessive rubbing or noises, eyeball the rotor and check it spins true, then pull the lever, the wheel should stop immediately.

-Lift the front and spin the wheel should move freely with minimal rub or noise, hopefully nothing, eyeball the rotor and check it spins true, then pull the lever, the wheel should stop immediately.

-Have a look at the pads, you need at least a few mm's of brake pad left. Be careful they wear out much quicker than rim pads, and extreme screeching sounds on the road it could mean the pads are worn through to the metal, it could damage the rotors and the shop might try to charge you for them. (At this stage I could take a plastic tire lever and push the brake pistons back into their bores and pull the lever to check that they are moving uniformly and are not dirty, but this is likely to annoy the shop mechanics).

-Go outside and do an emergency stop test at 30km/h or more.

That's probably too paranoid, the chances of both front and rear being bad is unlikely unless very bad mechanic has been doing maintence and has forgotten to pump the brakes after bleeding or something. Rental shops sometimes hate spending money on pads or other consumables and may forget to replace pads or bleed the system periodically.

andreas
Posts: 181
Joined: Thu Jun 12, 2014 10:21 pm

by andreas

Rubbing, contaminated pads/rotor (squealing and fading brake performance when getting hot), worn out pads. Easiest to check with a test ride before going on any group ride.

In a side note my last rental had a spacer stack that was well beyond manufacturers max limit, resulted in creaking headset because the stem was clamping onto hollow carbon tube instead of where the expander was. They had "compensated" by tightening the headset preload bolt to an insane torque. Scary stuff, could have snapped while on a descent.
Also, axle lever was in such a position that I accidentally undid it with my heel while pedaling.
Rental bikes are the worst :)

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Check if you have any pulsing from an improper bedding-in process. This may seem minor but it's annoying and perhaps even slightly dangerous at lower speeds, lower braking intensity if one section of a rotor is more grabby.

biwa
Posts: 161
Joined: Fri Sep 21, 2018 8:39 pm

by biwa

Some feedback from the trip. Had a few quick spins outside the shop during pick-up, braking seemed fine. Headed to the mountains and on the descent the front brake periodically did not engage, i.e. pull the levers easily all the way with little braking power. Scary. Not sure if this is a disc brake thing, but it seems testing brakes on the flat at lower speed may not be enough

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

biwa wrote:
Fri Sep 27, 2019 11:46 pm
Some feedback from the trip. Had a few quick spins outside the shop during pick-up, braking seemed fine. Headed to the mountains and on the descent the front brake periodically did not engage, i.e. pull the levers easily all the way with little braking power. Scary. Not sure if this is a disc brake thing, but it seems testing brakes on the flat at lower speed may not be enough

That is not normal and I can't imagine what would cause it. If there were bubbles in the brake system, it would have felt super mushy in all situations...or just not worked at all. If your pads are glazed or otherwise contaminated, the same thing applies. You’d feel it immediately the first time you tried to brake anywhere.

spdntrxi
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Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

TobinHatesYou wrote:
Sat Sep 28, 2019 12:03 am
biwa wrote:
Fri Sep 27, 2019 11:46 pm
Some feedback from the trip. Had a few quick spins outside the shop during pick-up, braking seemed fine. Headed to the mountains and on the descent the front brake periodically did not engage, i.e. pull the levers easily all the way with little braking power. Scary. Not sure if this is a disc brake thing, but it seems testing brakes on the flat at lower speed may not be enough

That is not normal and I can't imagine what would cause it. If there were bubbles in the brake system, it would have felt super mushy in all situations...or just not worked at all. If your pads are glazed or otherwise contaminated, the same thing applies. You’d feel it immediately the first time you tried to brake anywhere.
agree with THY.. disc brakes dont come and go... they pretty much work or they dont work well.

biwa
Posts: 161
Joined: Fri Sep 21, 2018 8:39 pm

by biwa

TobinHatesYou wrote:
Sat Sep 28, 2019 12:03 am
That is not normal and I can't imagine what would cause it. If there were bubbles in the brake system, it would have felt super mushy in all situations...or just not worked at all. If your pads are glazed or otherwise contaminated, the same thing applies. You’d feel it immediately the first time you tried to brake anywhere.
To add to the diagnosis of the problem, the problem I described was more prounounced when braking in the drops than on the hoods.

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Lewn777
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by Lewn777

biwa wrote:
Sun Sep 29, 2019 12:50 am
TobinHatesYou wrote:
Sat Sep 28, 2019 12:03 am
That is not normal and I can't imagine what would cause it. If there were bubbles in the brake system, it would have felt super mushy in all situations...or just not worked at all. If your pads are glazed or otherwise contaminated, the same thing applies. You’d feel it immediately the first time you tried to brake anywhere.
To add to the diagnosis of the problem, the problem I described was more prounounced when braking in the drops than on the hoods.
Sounds like the brakes were not properly bled with air in the system. I've found this worse with older SRAM systems, not sure why is would be worse from drops. If was in a Shimano system I would think it could be some kind of air leak.
*edit* Could the lever be damaged from a previous renter crashing?
Last edited by Lewn777 on Sun Sep 29, 2019 1:26 am, edited 1 time in total.

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

biwa wrote:
Sun Sep 29, 2019 12:50 am
TobinHatesYou wrote:
Sat Sep 28, 2019 12:03 am
That is not normal and I can't imagine what would cause it. If there were bubbles in the brake system, it would have felt super mushy in all situations...or just not worked at all. If your pads are glazed or otherwise contaminated, the same thing applies. You’d feel it immediately the first time you tried to brake anywhere.
To add to the diagnosis of the problem, the problem I described was more prounounced when braking in the drops than on the hoods.

The only difference between braking from the hoods and drops is mechanical leverage. So my suspicion is you just don’t understand how much more energy it takes to stop a rider+bicycle while descending vs on flat ground. The brakes are probably mushy in all conditions and you just didn’t notice during shakedown. They’re mush because they need a bleed, their reach adjust is wound in, their contact point adjustment was messed with or all of the above.

biwa
Posts: 161
Joined: Fri Sep 21, 2018 8:39 pm

by biwa

TobinHatesYou wrote:
Sun Sep 29, 2019 1:15 am
The only difference between braking from the hoods and drops is mechanical leverage. So my suspicion is you just don’t understand how much more energy it takes to stop a rider+bicycle while descending vs on flat ground. The brakes are probably mushy in all conditions and you just didn’t notice during shakedown. They’re mush because they need a bleed, their reach adjust is wound in, their contact point adjustment was messed with or all of the above.
That's possible. Braking at 20km/h and 60km/h is definitely different.

Regarding the cause(s) of this mushiness, could you expand on "their reach adjust is wound in, their contact point adjustment was messed with"? Thanks.

biwa
Posts: 161
Joined: Fri Sep 21, 2018 8:39 pm

by biwa

Lewn777 wrote:
Sun Sep 29, 2019 1:09 am
Sounds like the brakes were not properly bled with air in the system. I've found this worse with older SRAM systems, not sure why is would be worse from drops. If was in a Shimano system I would think it could be some kind of air leak.
*edit* Could the lever be damaged from a previous renter crashing?
The levers were intact, and it was Shimano Ultegra.

by Weenie


bm0p700f
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by bm0p700f

Normal checks. Check the brake feel fine, headset is not tight or has play. Check it simply works. Any.ore and your worrying to much. If you worry that much take your own bike.

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