The all-new Shimano Deore XT M8100 series of derailleurs brings a new level of drivetrain silence thanks to decreased tension in the low gear position and an added bumper on the pulley cage. Larger 13T pulleys increase efficiency and chain management while compatibility with SHIMANO's new 12-speed cassettes boosts range.
|MAX FRONT DIFFERENCE||0|
|MOUNT||Direct attachment (conventional)/Direct mount compatible|
|TENSION PULLEY BEARING||Sealed Bearing|
|GUIDE PULLEY BEARING||Sealed Bearing|
|NUMBER OF PULLEY TEETH||13|
|MAX LOW SPROCKET||51t|
|MIN LOW SPROCKET||45t|
|TOP NORMAL SPRING TYPE||Shimano Shadow RD+|
Please reach out to us with any questions you may have on anything we sell. We want to make sure you get the right part the first time. Our lifelong riders at Thunder Mountain Bikes are knowledgeable and would love to talk to you!
We currently offer both economy and expedited shipping options though FedEX and USPS.
Orders totaling over $49 are eligible to ship for free via an economy ground option of our choice.
If you're in need of something super-quick, please contact us directly. We may be able to overnight your order with an additional fee and depending on your location.
Should there be an issue with the item you bought, or you no longer need your purchase, we will be happy to set up a return.
All returns must be requested within sixty (60) days of the fulfillment date (i.e. the date we printed the shipping label and boxed up your order.) All returned items must be received in new and unused condition, with the original tags and labels attached, and in the original packaging. We cannot accept returns on any items that have been installed or show wear of any kind.
To request a return, please visit: returns.thundermountainbikes.com and follow the steps to return eligible items from your order.
After receiving your return and inspecting the condition of your item, we will process your return. Please allow at least seven (7) days from the receipt of your item to process your return or exchange. We will notify you by email when your return has been processed.
For all Special Order items, there is a 25% restocking fee. Special Order items are those that we do not currently stock.
For defective, damaged, or if we sent you the wrong products, please contact us using the phone number or email below.
If you have any questions concerning our return policy, please contact us at:
This is a beautiful piece of machinery. It works flawlessly and is easy to setup.
When there was no availability I ordered one of these on EBay from China and it never shifted correctly. I’m guessing it was an (expensive) counterfeit. I removed it today and put the new one from Thundermointainbikes today and it’s like butter. I have two of these from Thunder, so a fresh one and a spare. Along with the XTR chains that were on sale last week I’m set for a couple of weeks worth of crashes. 😂
They had the part I need it and processed and shipped ASAP. I was back on the bike in no time.
This was an upgrade on my Orbea OIZ H30 which came with a Shimano Deore RD-M6100 rear derailleur and shifter (I also upgraded to the XT shifter, which I purchased locally). The Deore XT parts perform much better - smoother, quicker shifting and a more solid feel overall, especially when downshifting. Definitely a good upgrade, and Thunder Mountain offered a competitive price and fast free shipping. I'm considering an upgrade to the XT cassette as well, but so far the change has been awesome already. 5 stars all around!
One of the best places to shop for Mountain bike parts, great service
Bought an XT to replace my shattered XTR derailleur - Thunder Mountain had it in stock and shipped it fast.
Pro tip: A carbon cage plate and parallelogram linkage on the XTR model save 44 grams, but when you clip the very edge of the derailleur parallelogram on a rock, the whole thing cracks into pieces. XT, on the other hand, is aluminum. Yeah, it's an ounce and change heavier, but more durable than my ill-fated XTR mech. Both of 'em function the same - put it on the bike, dial it in, and you're good to go - shifting is rock solid and perfect every time.