cycling
26. September, 17:53 Uhr
After some deliberation in [this thread](https://www.reddit.com/r/cycling/comments/9gtgee/brake_caliper_upgrade_tektro_r540s_to_tiagra/) about suitability of these calipers with my Tiagra 4700 brake levers, I've recently sourced and last night fitted a pair of Shimano 105 5800 series calipers to my Boardman Team Carbon in place of the original Tektro R540s.
Below is a summary for anyone interested - the Boardmans are a popular bike on this side of the pond and the 5800 calipers are a bargain currently thanks to the release of the 7000 series subsquent clearance of the older line.
It's been a long time since I changed a pair of calipers but I took my time, used the right tools and consulted internet grown-ups when necessary..
**Front**
I'd not considered the need to remove the ally cable-end, but furtunately (or indeed not as will be seen later) this came off with just my fingers, the cable clamp slackened off and the cable withdrawn from the caliper.
The front caliper came off after some consternation since its mounting bolt was stuck inside the fork. This was got out by re-fitting the nut on the rear a little and tapping it forward via a the 3/8" drive hex-driver I used to unscrew it. Note that the nut is recessed pretty deep inside the fork and you won't reach it with the short end of a conventional allen key.
The new front caliper came with 5 nuts of different lengths. I tried all in turn in the forks (without the caliper) from longest to shortest to find the correct one. They should bottom out inside the forks on their flange at the rear, not their front edge - the heads of those that were too long sat further back in the hole in the forks than the shorter ones. Eventually when the shorter ones start registering on the flange, all sizes seat in the forks to the same depth. I used the longest of these; which was reassuringly the closest in size to the nut that came off my old calipers.
The new caliper was fitted to the frame with no dramas; the shoes were pretty much where they needed to be and the caliper was held in the closed position against the rim while its retaining bolt in the fork was nipped up, in an effort to centre it (which worked well).
The brake cable was re-routed through the new caliper; which is where another problem was encountered. The Jagwire cables fitted to the bike wouldn't seat in the threaded cable adjustor on the caliper - their OD being around 5.6mm, the hole in the adjustor being 5.45mm. Since the bike was now unrideable and I wanted to get the job done, I swapped the cable adjustor over from the old Tektro calipers (6.1mm ID) which fitted fine as they apparently share the same (M6?) thread.
The cable was clamped into a suitable position with it held nearly closed. Shoe postions were set by slackening off their retaining bolts and moving them into correct positioning on the rim while maintaining some pressure on the brake lever; holding them gently in contact with the rim and stop them moving, before being nipped up.
**Rear**
The rear was more straightforward; knowing what I did about the adjustor / wire issue I undid the cable clamp and just unscrewed the whole adjustor from the caliper without removing it from the cable / having to remove the ally finisher crimped onto the end.
The caliper came off without sticking and was replaced with the new one. The original Tektro cable adjustor was screwed into the new caliper with a touch of oil on the threads.
Another problem was then encountered; in that the adjustor sits lower on the 105s than it did on the R540s - meaning the cable should by rights be a bit longer. I managed to draw the cable outer through the frame by maybe 15-20mm, which gave me enough to correctly sit inside the cable adjustor. Thankfully there was still enough cable at the front of the bike to prevent it rubbing the frame, unless the steering was turned to 90 degrees but I don't ever intend riding like that!
The rear caliper was set up the same as the front and I went out for a test ride.
​
**First Impressions**
When applying progressively more force to the Tektro brakes on the stationary bike significant flex could be seen in the arms of the caliper; making the brake operation feel spongy. The 105s still suffer this to an extent, however not as much.
In addition the 105s definitely have a lot more "bite" so less force is required at the brake lever to stop. Maximium braking force seems significantly higher with the 105s - with the Tektros you'd apply a fair bit of force and feel like any more wasn't really going to stop you any quicker, while with the 105s there seems like a better, more linear relationship between force input at the lever and output at the rim.
While both front and rear brakes feel significantly better than the Tektros they replaced, the rear feels more spongy than the front - I suspect because of its longer cable length (more stretch) and / or less current pad bearing area.
Out on the test ride the brakes feel noticeably less spongy and more effective for the lower levels of force required at the lever; both of which inspire more confidence and plays well with the bike's responsiveness in terms of accelerating in other directions (forwards and corners).
When the original calipers were removed I noticed that some of the wear surfaces of the pads were untouched, presumably because the pads had not sufficiently bedded in yet. I assume this will also be the case with the Shimanos too, so expect braking performance to improve with use.
I also measured the ratios between input cable travel and output caliper travel - a bit of a bodge as it approximated angular movement as linear, but gave a reasonable idea. The Tektros gave a ratio of 1.66:1 cable travel to change in distance between the two pads, while the Shimanos gave around 1.61:1. In the real world next to no difference; and one that could be explained away as measurement error in any case.
**Conclusion**
While not quite a 100% straight swap I'm very happy with the new calipers - they've increased braking performance markedly and were (IMO) well worth the £40 or so that the pair cost me. If you're in a similar situation with less-than-great Tektro originals with Tiagra 4700 shifters ( I don't think they'll work with 4600 and earlier) I'd suggest it's a well-worthwhile upgrade before the old stock of bargain 105 5800 calipers is exhausted ;)
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